This invention relates to electric lamps and, in particular, to a holder for an amalgam in a gas discharge lamp.
Maintaining mercury vapor pressure equilibrium within a gas discharge lamp such as a fluorescent lamp is necessary to maintain optimum lumen output during extended lamp on periods. In conventional fluorescent lamps, the mercury vapor pressure increases to an optimum pressure allowing the lamp to reach maximum lumen output. As time passes, the mercury vapor pressure increases to a level above the most preferable pressure causing the luminous flux to decrease.
To help maintain the pressure at the optimum pressure, amalgams are introduced to maintain the mercury vapor pressure within an optimal range during lamp operation. Upon lamp ignition, the amalgam is heated which causes mercury to diffuse out of the solid and is released into the lamp as vapor. The amalgam achieves mercury vapor equilibrium during lamp operation by supplying the same amount of mercury atoms to the interior of the lamp envelope as are spent. However, when the lamp is switched off, the decrease in temperature causes the mercury vapor to navigate to and diffuse into the amalgam causing mercury starvation. The lack of mercury vapor in the lamp envelope during off periods results in low lumens at lamp startup. In order to obtain peak lumens upon lamp ignition without any startup time penalty, an adequate dose of mercury vapor is required to remain in the lamp envelope during lamp off periods.
A restricted fixed orifice in an amalgam capsule can be used to reduce the starvation effect for short off times. U.S. Pat. No. 5,828,169 uses such a technique. However, during extended off times, virtually all of the mercury can still return to the amalgam.